Java Anonymous Classes and Lambdas

BatchTestingMachine.java

import java.util.ArrayList;
import java.util.List;

/***
 * Tests collections of samples all at once.
 */
class BatchTestingMachine {
	public List<String> processBatch(List<PatientSample> batch, ImmunityTest test) {
		List<String> results = new ArrayList<>(batch.size());

		for(PatientSample sample : batch){
			String result = generateResult(sample, test);
			results.add(result);
		}

		return results;
	}

	private String generateResult(PatientSample sample, ImmunityTest test) {
		return sample.getName() +
		       (test.isImmune(sample)
		        ? " has a clean bill of health!"
		        : " is sentenced to quarantine.");
	}
}

Covid19ImmunityTest.java

/***
 * An immunity test tailored to Covid19.
 *
 * Author's caveat: do not take this as a realistic test. This is entirely fictitious. :)
 */
class Covid19ImmunityTest implements ImmunityTest {
	@Override
	public boolean isImmune(PatientSample sample){
		return sample.hasTCellMemory() || sample.hasAntibodyDensityOver(0.2);
	}
}

ImmunityTest.java

/***
 * A test, returning whether a sample indicates immunity to some disease.
 */
@FunctionalInterface
interface ImmunityTest {
	boolean isImmune(PatientSample sample);
}

PathA.java

import java.util.Arrays;
import java.util.List;

/***
 * Path A - Use a named class for our test.
 */
public class PathA {
	public static void main(String[] args){
		List<PatientSample> batch = Arrays.asList(
				new PatientSample("Alfred", 0.2, false),
				new PatientSample("Betty", 0.5, false),
				new PatientSample("Carlos", 0.1, true),
				new PatientSample("Dietrich", 0.05, false),
				new PatientSample("Evans", 0.9, true),
				new PatientSample("Fran", 0.0, false)
		);

		BatchTestingMachine machine = new BatchTestingMachine();

		ImmunityTest test = new Covid19ImmunityTest();

		List<String> results = machine.processBatch(batch, test);

		for(String result : results) {
			System.out.println(result);
		}

		/*
		Output:

		Alfred has a clean bill of health!
		Betty has a clean bill of health!
		Carlos has a clean bill of health!
		Dietrich is sentenced to quarantine.
		Evans has a clean bill of health!
		Fran is sentenced to quarantine.
		 */
	}
}

PathB.java

import java.util.Arrays;
import java.util.List;

/***
 * Path B - Use an anonymous class for our test.
 */
public class PathB {
	public static void main(String[] args){
		List<PatientSample> batch = Arrays.asList(
				new PatientSample("Alfred", 0.2, false),
				new PatientSample("Betty", 0.5, false),
				new PatientSample("Carlos", 0.1, true),
				new PatientSample("Dietrich", 0.05, false),
				new PatientSample("Evans", 0.9, true),
				new PatientSample("Fran", 0.0, false)
		);

		BatchTestingMachine machine = new BatchTestingMachine();

		ImmunityTest test = new ImmunityTest() { // Note this new class doesn't have a name of its own!
			@Override
			public boolean isImmune(PatientSample sample){
				return sample.hasTCellMemory() || sample.hasAntibodyDensityOver(0.2);
			}
		};

		List<String> results = machine.processBatch(batch, test);

		for(String result : results) {
			System.out.println(result);
		}

		/*
		Output:

		Alfred has a clean bill of health!
		Betty has a clean bill of health!
		Carlos has a clean bill of health!
		Dietrich is sentenced to quarantine.
		Evans has a clean bill of health!
		Fran is sentenced to quarantine.
		 */
	}
}

PathC.java

import java.util.Arrays;
import java.util.List;

/***
 * Path C - Use a lambda for our test.
 */
public class PathC {
	public static void main(String[] args){
		List<PatientSample> batch = Arrays.asList(
				new PatientSample("Alfred", 0.2, false),
				new PatientSample("Betty", 0.5, false),
				new PatientSample("Carlos", 0.1, true),
				new PatientSample("Dietrich", 0.05, false),
				new PatientSample("Evans", 0.9, true),
				new PatientSample("Fran", 0.0, false)
		);

		BatchTestingMachine machine = new BatchTestingMachine();

		ImmunityTest test = (PatientSample sample) -> sample.hasTCellMemory() || sample.hasAntibodyDensityOver(0.2);

		// OR, even simpler:
		//
		// ImmunityTest test = sample -> sample.hasTCellMemory() || sample.hasAntibodyDensityOver(0.2);

		List<String> results = machine.processBatch(batch, test);

		for(String result : results) {
			System.out.println(result);
		}

		/*
		Output:

		Alfred has a clean bill of health!
		Betty has a clean bill of health!
		Carlos has a clean bill of health!
		Dietrich is sentenced to quarantine.
		Evans has a clean bill of health!
		Fran is sentenced to quarantine.
		 */
	}
}

PatientSample.java

/**
 * Data from a sample we've taken from a patient.
 */
class PatientSample {
	private final String name;
	private final double antibodyDensity;
	private final boolean hasTCellMemory;

	public PatientSample(String name, double antibodyDensity, boolean hasTCellMemory){
		this.name = name;
		this.antibodyDensity = antibodyDensity;
		this.hasTCellMemory = hasTCellMemory;
	}

	public String getName(){
		return name;
	}

	public boolean hasAntibodyDensityOver(double minimum){
		return antibodyDensity >= minimum;
	}

	public boolean hasTCellMemory(){
		return hasTCellMemory;
	}
}